Which of the following environmental variables represents the PID value of the last child process?

A.
$?

B.
$!

C.
$!!

D.
$$

Explanation:

The $! environmental variable represents the PID value of the last child process.
Answer option D is incorrect. The $$ environmental variable represents the PID of the running
shell.
Answer option A is incorrect. The $? environmental variable results in the value zero if the last
command was executed successfully, otherwise it displays the value one.
Answer option C is incorrect. It is an invalid Linux standard environmental variable.